Methods of grinding or polishing elongated rotational bodies



Aug. 27, 1963 0. Am; WALDEMAR 'SKUGGHALL 3,101,577

METHODS OF GRINDING OR POLISHING ELONGATED ROTATIONAL BODIES Filed Sept.10, 1962 5 Sheets-Sheet 1 IA/I/E/VTOB OSCAR A/\ E WALDEMAB JKUGGHALL EvW W Aug. 27, 1963 0. Km: WALDEMAR SKUGGHALL 3,

METHODS OF GRINDING OR POLISHING ELONGATED ROTATIONAL BODIES Filed Sept.10, 1962 3 Sheets-Sheet 2 //VVN7 0, OSCAR A/(E WALDEMAB SKUGGHALL 27,1963 o. A KE WALDEMAR SKUGGHALL 3,101,577

METHODS OF GRINDING OR POLISHING ELONGATED ROTATIONAL BODIES Filed Sept.10, 1962 5 Sheets-Sheet 3 f/VVf/V/ZE 050%? 19x5 Mmzmwiwgwaz UnitedStates Patent 3,101,577 METHODS OF GRINDING 0R POLISHING ELONGATEDROTATIONAL BODRES Oscar Ake Waldemar Skugghall, Jonkoping, Sweden,

assignor to Aktiebolaget Nydals Gjuteri och Mekaniska Verkstad, V.Holmgatan, .lonkoping, Sweden Filed Sept. 10, 1962, Ser. No. 222,492

Claims priority, application Sweden Sept. 18, 1961 2 Claims. (Cl.51-28%) The present invention relates to a method of grinding orpolishing elongated rotational bodies which, while being rotated abouttheir longitudinal axis, are advanced in engagement with a movablegrinding or polishing member, each part of which is caused to movesubstantially parallel to the longitudinal axis of said body at a speedconsiderably superior to that by which the body is advanced.

The chief object of this invention is achieving, so far as possible, andin a simple, nonexpensive way, a smooth and even surface of an elongatedrotational body by grinding 'and/ or polishing.

This object, as well as others, is accomplished by the method accordingto the present invention in which each part of said grinding orpolishing unit in momentary engagement with the body has had a speedcomponent imparted to it, which is substantially perpendicular to thelongitudinal axis of said body and which, with regard to its magnitudeand direction, is in substantial agreement with the circumferentialspeed of said body caused by its rotary motion, and in which each partof the grinding or polishing unit, while in momentary engagement withsaid body, is caused to work the latter along a path which is longerthan the distance that said body is advanced during each revolutionabout its longitudinal axis.

Further objects and advantages of the invention will become more fullyapparent from the following description and the accompanying drawingsillustrating preferred embodiments of the invention, and in which:

FIG. 1 is a perspective view showing how to work a tube by utilizing themethod according to the invention, as well as elements directlyco-operating with the tube in a machine intended for carrying out thismethod;

' FIG. 2 is a side view of a grinding or polishing apparatus in the formof a polishing disc, by the aid of which the surface of an elongatedrotational body, in the form of a tube, may be treated; and

FIG. 3 is a plan view corresponding to FIG. 2.

FIG. 4 illustrates an alternative embodiment in the same way as FIG. 2.

RIG. 5 illustrates a modification of the embodiment according to FIG. 1.

Referring particularly to FIG. 1, an elongated rotational body in theform of a tube '1 resting on a rotary roller 2, is rotated by means oftwo rollers 3, in the direction of the arrow N at a circumferentialspeed of N meters/sec. which corresponds to the rate of n revolutionsper second. These rollers 3 are slightly skewed, so that they impart bymeans of their rotary motion, a longitudinal motion to the tube, whichis thus advanced to the right at a rate of V meters per second, asindicated by the arrow V in FIG. 1. During the rotary and forwardmotions of the tube 1, its surface is worked by a grinding or polishingmember shown in FIGS. 1-3 and 5 of the drawings in the form of apolishing disc 4, but which might just as well be e.g.

an abrasive belt 8 which is held firmly pressed against the tube 1 by acontact disc 4a corresponding to the polishing disc 4 as shown in FIG.4. The tube 1 is supported by the rotary rollers 5 located opposite tothe grinding or polishing member. For the sake of simplicity, the termgrinding member will be used in the following description as a generaldesignation for the abrasive belt unit with appurtenant contact disc,polishing discs, grinding discs and similar tools used for surfacetreatment.

According to the invention, a motion is imparted to the grinding member,that is the polishing disc 4 or the combination of contact disc 4a andbelt 8 respectively, in such a manner that those patrs of it that are ininstantaneous engagement with the workpiece 1, are made to movesubstantially parallel to its longitudinal direction, at a speed of Wm./sec., when working its surface, as is indicated by the arrow W in thefigures. Consequently the grinding member 4 in FIG. 1 is rotated on theaxis 6 at a rate corresponding to circumferential speed of W m./sec.

Owing to the elasticity, among other things, of the grinding member(i.e. the elasticity of the polishing disc or contact discrespectively), the contact between the elongated rotational body, i.e.the tube 1, and the grinding member is not confined to a point butforms, in the example shown, a substantially elliptic contact area,designated with 7 in FIG. 3 and having a length of a meters and a widthof b meters. The shape and size of the contact [area above all depend onThe hardness of the grinding member, which affects both a and b;

The magnitude of the grinding pressure applied, which also afiects botha and b;

The diameter of the grinding member, which affects b; and

The diameter of the workpiece, which aifects b.

A hard grinding member naturally gives a smaller contact area than doesa soft one, using one and the same pressure. The shape of the grindingimage obtained will be aifected by the hardness of the grinding memberso that a hard contact disc will produce an image 7 having a morepointed appearance than a softer contact disc of equal diameter.Correspondingly, heavy working pressure produces larger contact areathan reduced working pressure, hardness of grinding member beingidentical. The amount of working pressure to be applied on the workpiecedepends on many factors, such as the condition of the workpiece, thegrain of the abrasive belt, the quantity of material to be removed, thehardness of the contact disc, etc.

The diameter of the grinding member (or that of the contact discrespectively) will afiect the size of the grinding image in about thesame way as will the hardness of the contact disc.

The larger the grinding member, the larger the grinding image produced,and vice versa the use of smaller grinding members will of course affectthe grinding pattern in the opposite way.

The number of revolutions of the contact isc will influence the resultof the grinding operation in such a way, among others, that its hardnessshall increase with the number of revolutions. The circumferential speedW giving the best possible belt ecenomy should be chosen. Concerning thenature of the face (whether plain or sernated face of the contact disc),the condition here is the one applicable in flat finishing: A plain discface produces a somewhat smoother surface, with less removal ofmaterial, however, but a serrated one gives a coarser surface but[achieves a larger amount of material removed.

In order to ensure treatment of the entire tube surface, and not only ofa helical path of it, it is essential that the advancement of the tubefor each revolution should beshorter than the length of the area 7. Inother words, the contact area 7 which is obtained at a certain tubeangle, must necessarily overlap the corresponding surface obtainedduring the preceeding revolution (with respect to the rotation of thetube). The above condition may be expressed by the following formula:

giving the following number of revolutions to be imparted to the tube:

The diameter of the tube 1 (or the workpiece) will aifect the dimensionsof the grinding image or the contact area. 7 in such a way that a largerdiameter of the tube 1 will give a greater value of b than will asmaller diameter, and vice versa if other conditions remain identical.

If the tube 1 is advanced at a comparatively high speed, V m./sec.,rather long striae will appear on its surface, and on account of itsrevolving motion, these will be slightly curved, giving the tube aspiral appearance. Even a slight skew of the polishing disc 4, orcontact disc 4a, (1 to 3 owing to the rotational speed N of the tube 1and to its feed speed V) will eliminate the helical path of the grindingpattern.

Because of this skew, the points of the grinding member being inmomentary contact with the tube 1, are imparted a speed componentsubstantially perpendicular to the longitudinal direction of the tube.This speed component is in substantial agreement with thecircumferential speed N of the tube, produced by its rotation.

The angle mentioned above (a) between the longitudinal axis of the tubeand that direction in which the different points of the surface of thegrinding member :move, when in contact with the tube 1, may becalculated with the use of the following formula:

tg L

W-i-V in which the designations have been used as going.

In accordance with another feature of the present invention the grindingmember is displaced substantially perpendicularly to the longitudinalaxis of the rotational body being processed, in order that fresh, unwornabrasive may be constantly brought into engagement with. it, as theabrasive on one part of the grinding member gets dulled or used up. Thisrelative displacement between the grinding member and the body beingprocessed, may be carried out intermittently or continuously and beperformed by moving either the grinding member or the rotational bodylaterally, or by a combination of both. This displacement which may beperformed, manually or automatically, by means of some means known perse, normally requires a width B (FIG. 3) of the grinding member, severaltimes larger, or at least essentially larger, than the width b of thecontact area 7. When the grinding unit is an abrasive belt, the lateraldisplacement of the belt may be performed continuously at such a ratethat the cutting or grinding capacity of the belt is entirely exhausted,as the entire width of the contact area in the foreor part of theworkpiece has been traversed. This also produces the effect that thedepth of the striae of the grinding pattern will gradually decrease asthe abrasive grains are worn down, and therefore a smoother surface willbe obtained than one normally obtained with the use of the chosen grainsize.

If the grinding member is comprised of a polishing disc, the rate of thelateral displacement chosen should be the one that dispenses of take upadjustments before its entire width has traversed the contact area, or acertain part of the workpiece (for instance all of it).

The choice of the kind of grinding member (type and grain size of theabrasive belt) is determined, as is the feed speed and the number ofpasses, by the material of the workpiece (whether stainless steel,aluminium, brass and so forth) and by the condition of this material(whether it presents more or less deep scratches etc).

The number of revolutions of the rotational body is intimately relatedto the appearance of the grinding pattern, i.e. of the contact area 7,and therefore indirectly dependent of the applied work pressure and thehardness of the contact disc and the feed speed etc.

While the invention has been particularly shown and described withreference to the preferred embodiments of FIGS. l-4, it will beunderstood by those skilled in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention. For instance, the rollers 5 in FIG. 1 might bereplaced by a second grinding member 41), workiug the surface of therotational body 1 in an identical way to that of the grinding orpolishing disc 4, and located diametrically opposite to the latter withrespect to the workpiece as shown in FIG. 5.

What I claim is:

1. A method of finishing the surface of an elongated rotational body,comprising the steps of advancing said body in the direction of itslongitudinal axis and in engagement with an abrasive member whilerotating said body on its said axis; moving each part of said abrasivemember in momentary contact with said rotational body at a speed whichis considerably superior to that by which said body is advanced, and ina direction which is substantially parallel to the longitudinal axis ofsaid rotational body but which has a component which, as to magnitudeand direction, is in substantial agreement with the circumferentialspeed of said body caused by its rotation; and maintaining the momentaryengagement between each part of said rotational body and said abrasivemember along a path which is longer than the distance that said body isadvanced during each revolution about its longitudinal axis.

2. A method as claimed in claim 1 further comprising the step ofdisplacing said abrasive member in its entirety With respect to saidrotational body during the surface finishing operation substantially atright angles to the longitudinal axis of said body through a distancesubstantially superior to the width of the contact area between saidmember and said body as measured in the direction of displacement ofsaid abrasive member so that fresh parts of said abrasive member whichhave not been in prior contact with said body are brought into repeatedcontact with said body.

References Cited in the file of this patent UNITED STATES PATENTS1,826,364 Drake et. a1. Dec. 15, 1931 1,988,577 Scrimgeour Jan. 22, 19352,935,822 Winchester et al. May 10, 1960 3,066,452 Bott et al. Dec. 4,1962

1. A METHOD OF FINISHING THE SURFACE OF AN ELONGATED ROTATIONAL BODY,COMPRISING THE STEPS OF ADVANCING SAID BODY IN THE DIRECTION OF ITSLONGITUDINAL AXIS AND IN ENGAGEMENT WITH AN ABRASIVE MEMBER WHILEROTATING SAID BODY ON ITS SAID AXIS; MOVING EACH PART OF SAID ABRASIVEMEMBER IN MOMENTARY CONTACT WITH SAID ROTATIONAL BODY AT A SPEED WHICHIS CONSIDERABLY SUPERIOR TO THAT BY WHICH SAID BODY IS ADVANCED, AND INA DIRECTION WHICH IS SUBSTANTIALLY PARALLEL TO THE LONGITUDINAL AXIS OFSAID